1. Field of the Invention
The present invention relates to an electromagnetic clutch device operated by a magnetic force of an electromagnetic coil.
2. Description of Related Art
There has been described a clutch device configured to switch between transmission and cutoff of a torque by electromagnetic means (see Japanese Patent Application Publication No. 2001-80385 (JP 2001-80385 A), Japanese Patent Application Publication No. 2010-164175 (JP 2010-164175 A), Japanese Patent Application Publication No. 2010-254058 (JP 2010-254058 A)).
A driving force switch mechanism described in JP 2001-80385 A is provided in a driving-force transmission path of a vehicle and functions as a clutch device for switching between a two-wheel-drive state and a four-wheel-drive state. The driving force switch mechanism includes an actuator including an electric motor and a speed reducer, a rack for converting a rotation of an output gear of the actuator into an axial displacement, and a sleeve spline-engaged with a first rotational member and a second rotational member due to an axial movement of the rack. When the first rotational member is connected to the second rotational member in a torque transmittable manner, a current is supplied to an electric motor so as to axially move the rack by the rotation of the output gear decelerated by the speed reducer, thereby causing the sleeve to be spline-engaged with the first rotational member and the second rotational member. Hereby, the driving-force transmission path of a drive source of the vehicle is switched, so that a drive state of the vehicle is switched from the two-wheel-drive state to the four-wheel-drive state.
Further, a tooth clutch described in JP 2010-164175 A includes a yoke for retaining an exciting coil, an armature drawn toward a yoke side by a magnetic force, and a pulley that rotate integrally with the armature by a biasing force of a leaf spring, and is configured such that a torque is transmitted by meshing between mound-shaped toothing portions formed on respective facing surfaces of the yoke and the armature.
A driving force transmission device described in JP 2010-254058 A includes: an actuator including an electric motor and a speed reducer; a pinion gear rotationally driven by the actuator; a shift rod driven axially via a rack gear meshed with the pinion gear; and a coupling sleeve to be switched between a coupled state in which the coupling sleeve is meshed with a clutch gear by reciprocation by a shift fork mounted in the shift rod and an uncoupled state in which the coupling sleeve is uncoupled from the clutch gear. The coupling sleeve and the clutch gear constitute a meshing clutch mechanism. In a state where the coupling sleeve is meshed with the clutch gear, a four-wheel-drive state where a driving force is transmitted to front and rear wheels is achieved. When the coupling sleeve is uncoupled from the clutch gear, a two-wheel-drive state where a driving force is transmitted only to the front wheels is achieved. Further, a spring for biasing the shift rod and the shift fork in a coupling direction where the coupling sleeve is coupled to the clutch gear is disposed between the shift rod and a case member.
At the time when the four-wheel drive state switches to the two-wheel-drive state, a pinion gear is rotationally driven by an electric motor, so that the coupling sleeve is meshed with the clutch gear against a biasing force of the spring. Further, at the time when the two-wheel drive state switches to the four-wheel-drive state, the shift fork is changed into a free state, so that the coupling sleeve is pressed against an end surface of the clutch gear by the biasing force of the spring, and when a rotation of the coupling sleeve is synchronized with a rotation of the clutch gear, the coupling sleeve is meshed with the clutch gear by the biasing force of the spring.